The invention relates to a closing device for a cylinder core turnable in a housing and a key insertable into a key channel. Such closing devices have been known for a long time as cylinder locks. The known constructions of such cylinder locks have, however, the disadvantage that with respect to locking safety and possibility of variation they no longer entirely meet current requirements. This is true particularly with respect to the construction of large locking systems in the conception of which many variation possibilities which theoretically exist are lost in actual practice. This is true under certain circumstances also of magnetic locks which operate on the basis of magnetic rotor holders. In the previous magnetic locks it, for e.g. space reasons, is not possible to increase the number of magnetic pills from three to four without substantially changing the dimensions which are customary for cylinder locks and their keys.